Protective device.



C. P STEHWVIETZx PROTECTIVE DEVICE.

APPLICATION FILED JUNE 19. 1913.

1,230,6 1 5. Patented June 19, 1917.

1 1 2 THESE/E5. JKZYENTUH 2'- M CHARLES E STEJNME'TA", 1% 44A. MMQM' H25A2" TUENEY.

UNITED STATES PATENT OFFICE."

CHARLES P. STEINMETZ, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

PROTECTIVE DEVICE.

Patented June 19, 1917.

i Application filed June 19, 1913. Serial No. 774,513.

To all whom may concern Be it known that 1, CHARLES P. STEIN- METZ, acitizen of the United States, residing atv Schenectady, county ofSchenectady,

State of New York, have invented certain new and useful Improvements inProtective Devices, of which the following is a specification.

My invention relates to protective devices for electrical installations,and in particular to devices for protecting electrical apparatus, suchas transformers, included in a high voltage electrical transmissionsystem.

A matter of reat importance in high voltage transmission systems is theprotec tion of the electrical apparatus, and in particular thetransformers, included in the system, from objectionable abnormaldisturbances. Such disturbances are caused by atmospheric discharges, byswitching, and by other abnormal phenomena. These disturbances are of anoscillatory character, usually of high frequency, and tend to build upwithin the system dangerous and destructive voltages. The objectionabledisturbances may arise withinthe apparatus, or more generally'theparticular section of the installation to be protected, or may arisewithout theapparatus. A protective device to be entirely satisfactorymust protect the apparatus regardless of the source of the disturbance.A protective device should, there fore, guard the apparatus against theentrance of objectionable disturbances, having their origin in thetransmission system, and should at the same time permit the exit intothe transmission system of all such disturbances originating within theapparatus itself.

The object of my invention is to provide a protective device which isselective in its action and permits a free flow of high frequencycurrents coming from one direction, but reflects such currents comingfrom the opposite direction. As applied to an electrical installationcomprising two sections, each having distributed resistance, inductanceand capacity, the object of my invention is to provide a protectivedevice which will permit the free exit of high frequency disturbancesarising within one section of the installation and will reflect backtoward the source high frequency disturbances arising in the othersection. In the application of my invention to a transformer, my objectis to protect the windings ofthe transformer against the entrance ofobjectionable disturbances from the transmission system, since suchdisturbances build up destructive voltages within the transformer. Atthe same time, my object is to provide a device which will allow thefree exit into the line or transmission system of an disturbanceoriginating within the transfbrmer, since otherwise such a disturbancewould by reflection increase in voltage, and therefore, indestructiveness.

Every oscillatory circuit, that is, a circuit having distributedcapacity and inductance, has a surge resistance of definite ohmic valuewhich is determined by the following formula, where R represents theohmic value of the surge resistance and L and C the inductance andcapacity in henries and farads respectively of the circuit:

The surge resistance may be defined as a resistance of such ohmic valuethat if the circuit is closed through this critical or surge resistanceany disturbance in the circuit passes into the resistance withoutreflection, while a higher, as Well as a lower, resistance causes apartial reflection of the disturbance back into'the circuit, thereflection being greater, the greater the resistance differs from thecritical value. The surge resistance is independent of frequency, andtherefore, the circuit which is closed through a resistance whose ohmicvalue is approximately equal to the ohmic value of the surge resistanceof the circuit, will permit afree passage of alternating currentregardless of the frequency of such current.

he surge resistance of the line conductors of a transmission systemisusually a few hundred ohms. The surge resistance of electricalapparatus is usually considerably higher. For example, the surgeresistance of transformers is usually several thousand ohms. Thisdifference in the surge resistance of transmission conductors andelectrical apparatus, in particular transformers, permits an arrangementof inductance and resistance which freely passes disturbances comingfrom the apparatus into the line, but

reflects practically completely any disturbance coming from the line,and so protects the apparatus from disturbances coming from eitherdirection.

In carrying out my invention I take advantage of the above describedcharacteristics of the surge resistance. I provide an arrangement ofinductance and resistance which in substance closes a circuit for theflow of high frequency currents through a resistance approximately equalin ohmic value to theohmic value of the surge resistance of theapparatus to be protected. To this end, I include in series with one ormore transmission conductors of the installation an inductance of ashigh value as is economically permissible and of negligible capacity.Each inductanceI shunt by a noninductive resistanceapproximately equalto the surge resistance of the apparatus to be protected.

The features which I believe to be patentably novel in'my invention aredefinitely indicated in the claims appended hereto.

The arrangement of apparatus inand the mode of operation of anelectrical installation embodying the. features of my invention will beunderstood from the following description takenin connection with theforegoing explanation and the accompanying The transformer idiagrammatically represented with a low voltage winding 1 and a highvoltage winding 2. The high voltage Winding is connected to atransmission system comprising line conductors 3. It will be understoodthat translating devices of any desired character maybe operativelyconnected to the conductors 3, but such de- 1 vices have been omitted'inthe drawings in order to secure slmpllclty 1n the showing.

' An'inductive winding or inductance 4 is included in series with a lineconductor 3 and is shunted by a resistance 5; The inductive winding -ihas as high inductance as permissible without offering any appreciableimpedance to .the flow of current of normal frequency. At the same time,the inductance issufliciently great to ofier substantially infiniteimpedance to the flow of high frequency currents. The resistance 5 hasan .ohmic value approximatelyequal to the ohmic value of the surgeresistance of the transformer. If the transformer has a capacity of Cfarads and an inductance of L henries, then the ohmic value of theresistance 5 should be approximately V 6 ohms. In the case of a typicaltransformer this surge resistance will be a few thousand' ohms. It willbe observed that the inducno oscillations whatever.

passes than the surge resistance B, so that the resultant of theresistance 5 and the effective hlgh frequency resistance of 4 equals thesurge resistance R.

The operation of my protective device will be understood, it isbelieved, from the foregoing explanation. The low frequency main workingcurrent passes through the induc tance 4 practically unimpeded. Due tothe very high ohmic value of the resistance 5,-

substantially no current of normal fre-.

quency passes through this resistance. High frequencydisturbances-cannot pass through the inductance 4, due to the enormousimpedance of the inductance for high frequency currents: Theinductancethus, in substance, forms an open circuit in the transmissionconductors for high frequency currents. This open circuit is, however,closed v through the resistance 5.

The surge resistance of the transmission conductors is onlya few hundredohms, and, therefore, any high frequency disturbance coming from theconductors will be reflected back again tothe source of such disturbanceby the inductance 4, and very little of I the disturbance willpassthrough the resistance 5 which is many times greater in ohmic value thanthe ohmic value of the surge resistance of the transmission conductors.On the other hand, a high frequency disturb ance comingfrom thetransformer is not reflected by the resistance 5, since this resistanceis approximately equal to the surge resistance of the transformer.Instead, any such disturbance from the transformer passes through theresistance and sets up disturbances originating in the transformer andpassing out through the, resistance 5 are dlsslpated in the resistance,or may be considered as let out into a line of infinite High frequency IThe unidirectional fea- Y ductance and capacity,

sion system. It will be understood that the greater the difference inthe value of the surge resistance of these sections, the more selectivewill be the action of my protective device.

I have herein explained in detail the principle and operation of myinvention and the manner of carrying the same into practical use.Numerous types and arrangementsof apparatus suitable for the purpose ofcarrying outmy invention will be apparent to those skilled in the art. Iaccordingly aim in the appended claims to cover all modifications andarrangements of apparatus withinthe spirit of my invention.

What I claim as new and desire tosecure by Letters Patent of the UnitedStates, is

1. The combination with an electrical installation comprising twoadjacent sections, the surge resistance of one section being ofdifferent ohmic value than the surge resistance of the other section, ofa resistance having an ohmic value approximately equal to the ohmicvalue of the surge resistance of one section, and means for directingthe flow of high frequency disturbances arising in either section tosaid resistance.

2. The combination with an electrical installation comprising twoadjacent sections each section having combined resistance inductance andcapacity, ofmeans operatively related to said installation and includingohmic resistance for permitting the free exit of high frequencydisturbances arising within one tion and for reflecting back toward thesource high frequency disturbances arising in the other section.

3. The combination with an electrical installation comprising twoadjacent sections, each section having combined resistance, in theinductance and -apacity of one section differing from the inductance andcapacity of the other section,means included in said installation forpractically open circuiting the installation to the flow of highfrequency current without offering substantial impedance to the flow ofcurrent of normal frequency, and a resistance in shuntrelation to saidmeans and having an ohmic value of such amount as to permit the freeexit of high frequency disturbances arising within one section of saidinstallation and to reflect back toward the source high frequencydisturbances arising in the other section.

"1'. The combination with an electrical installation comprisingtransmission conductors and an apparatus to bev protected, of aresistance approximately equal in ohmic.

value to the ohmic value of the surge re sistance of said ap'paratus,and means for directing the flow of high frequency disturbances to saidresistance.

5. The combination with an electrical insection of said installacomparedwith the ohmic value of the surge resistance of the transmissionconductors, of a non-1nductive resistance having an ohmic valueapproximately equal to the ohmic value of the surge resistance of saidapparatus, and means for directing the flow of high frequencydisturbances arising in said apparatus or in said transmissionconductors to said resistance.

7. The combination with an electrical i11- stallation comprisingtransmission conductors and an apparatus to be protected, said apparatushaving a surge resistanceof relatively large ohmic value compared withthe ohmic value of the surge resistance of the transmission conductors,of an inductance connected in series with a transmission conduct-or, anda non-inductive resistance having an ohmic value approximately equal tothe ohmic value of the surge resistance of said apparatus and connectedin shunt relation to said inductance; V 8. The combination with anelectrical installation comprising transmission conductors and atransformer, of means for permitting the free exit of high frequencydisturbances arising within the transformer and for preventing theentrance into the transformer of high frequency disturbances arisingwithout the transformer.

9. The combination with an electrical in stallation comprisingtransmission conductors and a transformer, of means included in saidinstallation for practically open circuiting the installation to theflow of "high frequency disturbances without offering substantialimpedance to the flow of current of normalfrequency, and a resistance inshunt relation to said means and having an ohmic value of such amount asto permit the free exit of high frequency disturbances arising withinsaid transformer, and to reflect back toward the source-high frequencydisturbances arising without said transformer. 7

10. The combination with an electrical installation comprisingtransmission conductors and a transformer, of a resistance approximatelyequal in ohmic value to the ohmic value of the surge resistance of saidtransformenand means for directing the 'the ohmic valueofthe surgeresistance of 10' flow of high'fre'quency disturbances to said saidtransformer and connected in shunt resistance. relation to saidinductance. I

'11. 'The co'mbination with an electrical in- In witness whereofll havehereunto set stallation comprising transmission conducmy hand'this 17thday of June, 1913.-

tors and a transformer, of an inductance CHARLES P. STEINMETZ. connectedin series with 'a transmission con Witnesses:

ductor, and a non-inductive resistance hav- BENJAMIN B. HULL,

ing an ohmic value approximately equal to HELEN ORFORD.

